Beep the Meep
Beep (also known as Beep the Meep) was the ruthless leader of the Meeps and a galactic criminal, who referred to himself as the Most-High.
In 1980, Beep led the Meep armada in an attempt to conquer the galaxy, but they were defeated by the Wrarth Warriors. Fleeing, Beep was pursued to Earth and his neutron drive star cruiser crashed at the Blackcastle steel mills. He was found by Sharon and Fudge, who assumed the cute creature was harmless, and took him back to Fudge's home. Meep then used his ship's black orb to took control of the people of Blackcastle to make them repair his ship. The Doctor sabotaged the engines, and Beep was captured by the Wrarth Warriors. (DWM: Doctor Who and the Star Beast)
In 1995, Beep was released from prison, having convinced the parole board that he had been rehabilitated. He returned to Blackcastle to retrieve his spare starship drive, but the Doctor trapped him within a Lassie film. (DWM: Star Beast II)
In the early 21st century, Beep escaped from the film, and hypnotised some television executives to air bad programmes such as Audience Shares. His goal was to hypnotise the viewing audience with subliminal messages on the debut episode of Meep and Friends, but he was once again defeated by the Doctor and arrested by security. (BFA: The Ratings War)
Years later, when a Vortex parasite attacked the Doctor's TARDIS, it summoned images of the Doctor's enemies, including Beep. (DWM: A Life of Matter and Death)
In a possibly apocryphal account, the Doctor and Izzy Sinclair traveled to another universe and again encountered Beep, attempting another hypnotic attack. Although Beep managed to capture the Doctor, Izzy was able to recruit the assistance of Tom Baker to act as a distraction long enough for her to reprogram Beep's machines and defeat him. (DWM: TV Action!)